Marcus Rashford's first-half strike at the Etihad Stadium saw his first Manchester derby end in a 1-0 win, making his manager believe a top-four finish is within their grasp.

"I have said in advance that we must win this game and we have done it, so I am very happy because otherwise the gap was too big if they won," Van Gaal said. "Or a draw is still four points, eight matches to go, so then it should be very difficult.

"Now it is in our own hands, I think. We have to win our games, we have more home matches than away matches. We don't lose so much at Old Trafford so we have a big chance."

Van Gaal says that the belief was palpable in the dressing room after a match which left him proud given Thursday's Europa League exertions.

"I think that we have played a fantastic first half," he said. "We started the second half again very good and had the first chances -- after that it was a test of survival because we were very tired.

"We have to recover within two days -- that is nearly not possible and especially not when you play a game against Liverpool like we have done.

Manchester United are now only a single point of the Champions League places.

"We have and have given everything to beat Liverpool and then you have to play City. You have seen, for example, their result at Southampton -- half-time 0-2, final time 3-2.

"I have not seen the match but I can only conclude that it is because of the tiredness. That is what we have done to them.

"My players have fought to the end with cramp -- Marcus Rashford could still run with cramp. I have never seen that!"

Van Gaal's comments came in response to a question about United targeting City's injury-hit defence.

While coy when asked about that in the news conference, he was far more forthcoming in the broadcast interviews, especially on City centre-back Martin Demichelis.

"Rashford is very quick and Demichelis looked like the years are catching up with him," he said. "He was a very good defender, he was my centre-back in Bayern but that is the life of football."